Composites having improved surface properties

ABSTRACT

Polymeric composite materials having a decreasing concentration gradient of polymer matrix from the material&#39;s surface to the material&#39;s interior and a process for making such materials, whereby polymer matrix is extracted from the interior of the material in such a manner that the matrix concentration at the material&#39;s surface increases.

The Government has rights in this invention pursuant to contract No. F33615-86-C-5069 awarded by the Department of the Air Force, Departmentof Defense.

This is a division of application Ser. No. 07/619,149, filed Nov. 28,1990 and issued as U.S. Pat. No. 5,178,812.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to polymeric composite materials havingimproved surface properties More particularly, the invention relates toa polymeric composite material having a decreasing concentrationgradient of polymer matrix from the material's surface to the material'sinterior. The invention also includes a process for extracting polymermatrix from the interior of a composite material in order to increasethe matrix concentration at the material's surface.

2. Description of the Prior Art

It is known that high modulus fibers, such as poly(p-phenyleneterephthalamide) aramid fibers, may be incorporated into polymer matrixmaterials to form composites. For example, United Kingdom PatentApplication, 2,195,672 A, published Apr. 13, 1988 discloses a processfor fabricating composites comprising forming a network of microfibrilsof a rigid polymer, a polymer which has the ability to form a liquidcrystalline phase either in a solution or melt, and interpenetrating themicrofibrils with a matrix material, such as a thermoplastic polymer, toform a composite.

Gabriel et al., coassigned, U.S. Pat. No. 5,000,898, the disclosure ofwhich is hereby incorporated by reference, discloses a process formaking oriented, fibers of lyotropicpolysaccharide/thermally-consolidatable polymer blends by spinning abiphasic solution containing at least about 55% and less than about 80%by weight of a lyotropic polysaccharide polymer, and at least about 20%and less than about 45% by weight of a thermally-consolidatable polymer.These fibers are particularly useful for composite applications.

Yang, coassigned, U.S. Pat. No. 5,011,643, the disclosure of which ishereby incorporated by reference, discloses a process for makingoriented, fibers of para-aramid/thermally-consolidatable polymer blendsby spinning a biphasic solution containing at least about 55% and lessthan about 80% by weight of a para-aramid polymer, and at least about20% and less than about 45% by weight of a thermally-consolidatablepolymer. These fibers are particularly useful for compositeapplications.

By, U.S. Pat. No. 4,810,735, the disclosure of which is herebyincorporated by reference, discloses fibers prepared from spinnabledopes comprising a first polymer selected from poly(paraphenylenebenzobisthiazole) (PBT); poly(paraphenylene benzobisoxazole) (PBO); orpoly-2,5-benzoxazole (AB-PBO) polymers, and a second polymer selectedfrom a thermoplastic polymer or intractable polymer in a combinedsolvent of poly(phosphoric acid) and methanesulfonic acid orchlorosulfonic acid. These fibers are particularly useful for compositeapplications.

However, it was found that composite fibers, particularly thosedisclosed in the foregoing Gabriel et al., Yang, and Uy references,often have a deficient concentration of polymer matrix on their surfaceswhich causes poor adhesiveness, particularly in a cross-ply compositeconstruction It is often desirable to have a high concentration ofpolymer matrix at the surface of a polymeric composite material in orderto improve adhesiveness, and other properties such as the surfacefinish. An objective of the present invention is to provide suchmaterials having a decreasing concentration of polymer matrix from thematerial's surface to the material's interior.

Another objective of the invention is to provide a process forextracting polymer matrix from the interior of a polymeric compositematerial in order to increase the matrix concentration at the material'ssurface.

SUMMARY OF THE INVENTION

The present invention relates to a process for extracting polymer matrixfrom the interior of polymeric composite materials such as oriented,shaped articles and plies. Preferably, the polymeric composite materialcomprises at least about 30% and less than about 80% by weight of areinforcing polymer phase consisting essentially of at least onelyotropic polymer, and at least about 20% and less than about 70% byweight of a polymer matrix consisting essentially of at least onethermally-consolidatable polymer The reinforcing polymer phase may becontinuous in the direction of orientation of the material, whileinterpenetrating the polymer matrix throughout the material, and thereinforcing polymer phase and polymer matrix may be co-continuous.Suitable lyotropic polymers include para-aramid and aromaticheterocyclic polymers Suitable thermally-consolidatable polymers includepolyimides and thermoplastic polymers, particularly thermoplasticpolyamides

The process comprises treating the material with a selective solventwhich dissolves the polymer matrix, while not substantially dissolvingthe reinforcing polymer phase. Suitable solvents forlyotropic/thermally-consolidatable blends include, for example, sulfuricacid, methanesulfonic acid, formic acid, and hexafluoroisopropanol. Thesolvent is then removed, whereby at least some of the polymer matrix isextracted from the interior of the material and the matrix concentrationincreases at the material's surface. The process of this invention mayalso be used to treat other polymer blends comprising a polymer matrixand reinforcing phase.

The invention also includes composite materials, which may be made fromthe foregoing process, having a decreasing concentration gradient ofpolymer matrix from the material's surface to the material's interior

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a optical micrograph (OM) at 50 ×of a longitudinal section ofa poly(paraphenylene benzobisthiazole)(PBT)/poly(ether ketoneketone)(PEKK) microcomposite ply which has not been treated with an acidicsolvent.

FIG. 2 is a optical micrograph (OM) at 50 ×of a longitudinal section ofthe microcomposite ply of FIG. 1 which has been treated with an acidicsolvent according to the present invention.

FIG. 3 is a scanning electron micrograph (SEM) at 500 ×of across-section of a poly(paraphenylene benzobisthiazole)(PBT)/polyamidemicrocomposite yarn which has not been treated with an acidic solvent.

FIG. 4 is a scanning electron micrograph (SEM) at 500 ×of across-section of the microcomposite yarn of FIG. 3 which has beentreated with an acidic solvent according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to polymeric composite materials having adecreasing concentration gradient of polymer matrix from the material'ssurface to the material's interior, and to a process for extracting atleast some of the polymer matrix from the interior of a compositematerial in such a manner as to increase the matrix concentration at thematerial's surface.

The polymeric, composite material comprises a polymer matrix andreinforcing phase. Preferably, the composite material comprises a blendof at least one lyotropic polymer, and at least onethermally-consolidatable polymer. By the term, lyotropic polymer, it ismeant a class of polymers which have a high persistence length andfunction as a "rigid rod" in solution. Suitable lyotropic polymersinclude, for example, aromatic polyamides and aromatic-heterocyclicpolymers with chain extending bonds from aromatic/heterocyclic groupswhich are either coaxial or are parallel and oppositely directed, andpolysaccharides with (1,4)-β-linkages in the backbone such as cellulose,cellulose derivatives, chitin, and chitin derivatives.

Preferably, the lyotropic polymers are para-oriented, aromaticpolyamides (para-aramids). The term, para-aramid, is meant to refer topara-oriented, wholly aromatic polyamide polymers and copolymersconsisting essentially of recurring units of formulas I and II below:

    --[NH--AR.sub.1 --NH--CO--AR.sub.2 --CO--]--               I

    --[NH--AR.sub.1 --CO]--                                    II,

wherein AR₁ and AR₂, which may be the same or different, representdivalent, para-oriented aromatic groups. By para-oriented, it is meantthat the chain extending bonds from the aromatic groups are eithercoaxial or are parallel and oppositely directed. Examples includesubstituted or unsubstituted aromatic groups such as 1,4-phenylene,4,4'-biphenylene, 2,6-naphthylene, 1,5-naphthalene, and4,4'--Ph--X--Ph-- or 3,4'--ph--X--Ph--, where Ph is a phenylene ring,and X is O, CO, S, SO₂, NH, NH--CO or (CH₂)_(n) with n=1-4. Suitablesubstitutents on the aromatic groups should be nonreactive and include,for example, chloro, lower alkyl and methoxy groups. The term,para-aramid, is also meant to encompass para-aramid copolymers of two ormore para-oriented comonomers, including minor amounts of comonomerswhere the acid and amine functions coexist on the same aromatic species,for example, copolymers produced from such reactants as 4-aminobenzoylchloridehydrochloride, and 6-amino-2-naphthoyl chloride hydrochloride.In addition, the term, para-aramid, is meant to encompass copolymerscontaining minor amounts of comonomers containing aromatic groups whichare not para-oriented, such as m-phenylene and 3,4'-biphenylene.

The inherent viscosity of the para-aramid in the preferred compositearticles should be greater than about 3 dl/g. The most preferredlyotropic polymer is poly(paraphenylene terephthalamide), PPD-T, havingan inherent viscosity of greater than about 4 dL/g.

Suitable aromatic-heterocyclic polymers include, for example,poly(paraphenylene benzobisthiazole) (PBT), poly(paraphenylenebenzobisoxazole) (PBO), and poly(paraphenylene benzobisimidazole)(PBIAB). PBO and PBT are particularly useful and preferably have anintrinsic viscosity of at least 15 dL/g.

Suitable polysaccharides with (1,4)-β-linkages in the backbone include,for example, cellulose, cellulose derivatives, chitin and chitinderivatives. These chain-extending (1,4)-β-linkages contribute to thepolymer exhibiting rigid rod-like behavior in solution.

By the term, thermally-consolidatable polymer, it is meant a class ofpolymers which can be consolidated by applying heat and pressureaccording to such mechanisms as melting, softening, and chemicalreactions. Preferably, thermoplastic polymers are used. Thesethermoplastic polymers include, for example, poly(ether ketoneketone)(PEKK); polyacrylonitrile(PAN); crystalline thermoplastic polyamides,such as poly(hexamethylene adipamide) and poly (ε-caproamide)); andamorphous thermoplastic polyamides. Polyimides may also be used.Amorphous thermoplastic polyamides are particularly useful for thepresent invention.

The oriented, shaped composite articles are formed by preparing asolution, or dope, of a polymer which will form a reinforcing polymerphase, e.g., a lyotropic polymer, and a polymer matrix, e.g., athermoplastic polymer, in a suitable solvent. The solution, or dope, maybe prepared by techniques known in the art, but it should be well-mixedin such a manner that it appears homogeneous to the unaided eye. Above acritical concentration of the lyotropic and thermally-consolidatablepolymers, the solution segregates into two coexisting phases, whereinone phase is optically anisotropic (liquid crystalline) and the otherphase is isotropic. The anisotropic domains primarily include thelyotropic polymer, while the isotropic domains primarily include thethermally-consolidatable polymer. The resulting solids concentrationshould also be such that the lyotropic polymer does not precipitate outof the solution. Generally, a solution concentration of 12 to 20 percentby weight of polymer is effective.

Preferably, the solvent dissolves enough of the lyotropic andthermally-consolidatable polymers to form a biphasic solution. Forpara-aramid/thermoplastic polyamide polymer blends, sulfuric acid havinga concentration between about 99 and 102 percent by weight is a suitablesolvent. For some polymer blends, it is necessary to use a mixedsolvent. For example, a combination of poly(phosphoric acid)andmethanesulfonic acid or chlorosulfonic acid, as disclosed in U.S. Pat.No. 4,810,735, can be used with PBT/thermoplastic polyamide andPBO/thermoplastic polyamide polymer blends. A mixed solvent oftrifluoroacetic acid and formic acid can be used for cellulosetriacetate/thermoplastic polyamide polymer blends.

For lyotropic/thermally-consolidatable blends, the reinforcing polymerphase comprises at least about 30 percent and less than about 80 percentby weight of the article and the polymer matrix comprises at least about20 percent and less than about 70 percent by weight of the article.Generally, it is necessary for the reinforcing polymer phase to containat least about 55 percent and preferably greater than about 60 percentby weight of the lyotropic polymer based on the combined weight of bothpolymers in order to obtain spinning continuity and high tensilestrength in the articles. Generally, it is necessary for the polymermatrix to contain at least about 20 percent by weight of thethermally-consolidatable polymer based on the combined weight of bothpolymers in order to facilitate consolidation of the articles.

The reinforcing polymer phase may be substantially continuous in thedirection of orientation of the article, while interpenetrating thepolymer matrix throughout said article. In a fiber or ply, wherein thedirection of orientation is longitudinal, the reinforcing polymer phase,as microfibrils, extends continuously along the length of the fiber. Forfibers or plies of the present invention, the orientation angle ispreferably less than 30°.

If the lyotropic polymer, PPD-T, is used, the articles preferably havean orientation angle less than 20°, and the reinforcing polymer phaseand polymer matrix are substantially continuous in the direction oforientation of the article.

In order for the reinforcing polymer phase containing the lyotropicpolymer to be continuous in the direction of orientation of the article,it is necessary for the reinforcing polymer phase and the polymer matrixto be finely-divided in the blend. The polymer matrix is preferablydistributed into domains having a width less than about 300 microns, andmore preferably less than about 100 microns. While this distribution canbe achieved by adding the polymers simultaneously to the solution andmixing with strong agitation over along period of time, it is preferableto first dissolve the less soluble lyotropic polymer in the solvent andthen subsequently add the more soluble thermally-consolidatable polymer.Prior to adding the thermoplastic polymer, the temperature of thesolution must be sufficiently high to insure that the melted solutiondoes not freeze and transform into a crystalline solvate. However, thetemperature should not be so high that the polymers degrade in solution.In order to prevent gross phase separation, it is usually necessary tocontinue agitating the solution, or to form the oriented, shapedcomposite articles shortly after the solution is prepared.

The solutions can be used to make oriented, shaped composite articles bysuch known techniques as forming fibers by spinning, extruding the dopeinto films, or fabricating the dope into fibrids. However, thesetechniques must be capable of removing the solvent from the highviscosity solutions which are typically greater than 100 poise. Suitabletechniques include, for example, air gap wet spinning and film extrusionprocesses, wherein the solution passes through a spinneret or die intoan air gap and subsequently into a coagulant bath, wherein the solventis removed from the solution. Generally, processes which produce hightenacity fibers and films from lyotropic polymers may be used in thepresent invention. The methods disclosed in Blades, U.S. Pat. No.3,767,756, which is hereby incorporated by reference, may also be usedto spin the fibers of the invention.

These oriented, shaped composite articles are then treated with anacidic solvent which selectively dissolves the polymer matrix but doesnot substantially dissolve the reinforcing polymer phase. If thereinforcing polymer phase comprises a lyotropic polymer and the polymermatrix comprises a thermoplastic polyamide, suitable solvents include,for example, sulfuric acid, methanesulfonic acid, formic acid, andhexafluoroisopropanol. Preferably methanesulfonic acid is used. If thereinforcing polymer phase comprises a lyotropic polymer, and the polymermatrix comprises a poly(ether ketoneketone) (PEKK) or a polyimide,sulfuric acid is preferably used.

These oriented, shaped composite articles, or "pre-forms", may then beconsolidated into bulkier composite materials by applying heat andpressure to the article. The acidic solvent treatment facilitates thisconsolidation process. Consolidation techniques involve, for example,placing fibers in an appropriate mold and compressing the fibers whilemaintaining a temperature at or above the melting point, glasstransition temperature, or reaction temperature of thethermally-consolidatable polymer. Composite materials such as compositeplies including cross-plies, laminates of cross-plies, unidirectionalcomposites, composites containing fabrics woven from fibers of theinvention, and composites from discontinuous fibers can be made by suchtechniques. Alternatively, the "pre-forms" may be consolidated intobulkier composite materials prior to acidic solvent treatment.

The period for treating the composite material with the solvent iscritical. If the period is too short, the polymer matrix will notdissolve sufficiently. However, if the period is too long, the polymermatrix and reinforcing phase, which dissolves more slowly than thepolymer matrix, will completely dissolve. Generally, the period oftreatment needed to dissolve the polymer matrix varies with thesolubility of the polymer matrix in a particular solvent, the treatmenttechnique, i.e, dipping, spraying, brushing etc., and the form ofcomposite material, i.e., yarn, ply etc. The solvent may be applied byconventional techniques such as by, dipping, spraying, or brushing,provided there is sufficient contact time between the solvent andcomposite material. Generally, a sufficient contact time for treating ayarn is between 3 to 60 seconds, and a sufficient contact time fortreating a ply is between 3 to 300 seconds.

The solvent is then removed from the composite material in such a mannerthat at least some of the polymer matrix is extracted from thematerial's interior and the matrix concentration increases at thematerial's surface. Since the process of extracting the matrix from thematerial's interior is by diffusion, the amount extracted, and theincrease of matrix concentration at the surface is a function of thelength of contact time. This extraction occurs in such a manner that adecreasing concentration gradient of polymer matrix forms from thematerial's surface to the material's interior This step of removing thesolvent and extracting the matrix is preferably performed by suchtechniques as immersing the material in an appropriate basic solutionand then rinsing the material with water until it is neutralized, orrinsing the material solely with water until neutralized. Alternatively,certain solvents may be removed by heating, or evaporating under ambientconditions. The solvent treatment and removal process of this inventionmay also be used to treat other polymer blends comprising a polymermatrix and reinforcing phase in order to extract at least some of thematrix from the material's interior and increase the matrixconcentration at the material's surface. The increase of polymer matrixat the material's surface provides for improved surface properties suchas adhesiveness, and the the concentration gradient of polymer matrixensures that the matrix is distributed throughout the material. Theseproperties make the material particularly useful for compositeapplications.

TESTING METHODS Fiber X-ray Orientation Angle

A bundle of filaments, about 0.5 mm in diameter, is wrapped on a sampleholder with care to keep the filaments essentially parallel Thefilaments in the sample holder are exposed to an X-ray beam produced bya Philips X-ray generator (Model 12045B) operated at 40 kv and 40 mausing a copper long fine-focus diffraction tube (Model PW2273/20) and anickel beta-filter

The diffraction pattern from the sample filaments is recorded on KodakDEF Diagnostic Direct Exposure X-ray film (Catalogue Number 154-2463),in a Warhus pinhole camera. Collimators in the camera are 0.64 mm indiameter. The exposure is continued for about fifteen to thirty minutes,or generally long enough so that the diffraction feature to be measuredis recorded at an Optical Density of ˜1.0.

A digitized image of the diffraction pattern is recorded with a videocamera. Transmitted intensities are calibrated using black and whitereferences, and the gray level is converted into optical density. A dataarray equivalent to an azimuthal trace through the two selectedequatorial peaks is created by interpolation from the digital image datafile; the array is constructed so that one data point equals one-thirdof one degree in arc.

The Orientation Angle is taken to be the arc length in degrees at thehalf-maximum optical density (angle subtending points of 50 percent ofmaximum density) of the equatorial peaks, corrected for background. Thisis computed from the number of data points between the half-heightpoints on each side of the peak. Both peaks are measured and theOrientation Angle is taken as the average of the two measurements.

Inherent Viscosity

Inherent Viscosity (IV) is defined by the equation: ##EQU1## where c isthe concentration (0.5 gram of polymer in 100 ml of solvent) of thepolymer solution and η_(rel) (relative viscosity) is the ratio betweenthe flow times of the polymer solution and the solvent as measured at30° C. in a capillary viscometer.

Intrinsic Viscosity

Intrinsic viscosity [n] is defined by the equation:

    [n]=[IV].sub.c=o

where [IV] is the inherent viscosity and c=o is zero concentration. Theintrinsic viscosity for PBT and PBO are measured in methanesulfonic acidat 30° C.

Domain Size in Spin Dopes

Spin dopes are examined with optical microscopy to determine thebiphasic nature of these solutions. For poly(paraphenyleneterephthalamide), polyamide, sulfuric acid dopes, samples are preparedby scraping a thin layer of solidified dope at room temperature. Thisthin layer is placed between two glass slides. The slides are set into aMettler FP82 hot stage which is held at about 90° C. When the dopemelts, the slides are pushed firmly together using hand pressure. Thisresults in a thin, translucent layer of solution. The sample is thenallowed to relax for about 1-1.5 hours. For a cellulose triacetate, PAN,nitric acid solution, the dope is placed between two glass slides. Thesample is pressed, using hand pressure, to facilitate a thin sample. Theedges of the slides are sealed with Parafilm to prevent loss of solvent.The sample is then allowed to relax overnight at room temperature.

The samples are observed with polarized and crosspolarized light using aNikon polarizing optical microscope equipped with a camera. It has beenshown that when static (relaxed) isotropic solutions are placed betweencrossed polarizing elements, they will essentially not transmit anylight. However, anisotropic dopes will transmit light and a relativelybright field is observed. Since these solutions are composed of twophases, one being isotropic and one being anisotropic, the two phasescan be distinguished by comparison of observation between polarized andcross polarized light. The samples may be viewed and photographed at100x using Polaroid type 57 3000 ASA film. The size of the isotropic andanisotropic domains are determined by measurement of the domains on thephotographs.

Composite Testing

The composite samples were tested for lap-shear strengths in an Instrontesting frame as described in Examples 2 and 9, infra.

Electron Spectroscopy for Chemical Analysis (ESCA)

A Perkin-Elmer PHI 5400 ESCA Spectrometer was used to determine thesurface composition and surface chemical functionality of the samples.

A survey spectrum was obtained after the sample was introduced into thespectrometer's vacuum chamber. From the peaks in the spectrum, theelements detected on the surface of the sample were identified. Then,high resolution spectra were obtained for the elements directed in thesurvey spectrum.

From the high resolution spectra, the binding energy of a given elementcan be obtained and after correction for charging it, the binding energycan be used to provide information on the functional group or oxidationstate of the element.

The atomic concentration (AC) of an element is the ratio of that elementto the sum of the other elements present (excluding hydrogen) in theacquired data. Elemental atomic concentrations are expressed aspercentages and are based on the area under the peak in the spectrum.The area under the peak is calculated from the absolute area under thepeak by subtracting the background and normalizing the area for the stepsize (set experimentally). The formula for calculating the atomicconcentration percentage is given by the following equation:

    AC for element x=[(Ix/SxTx)/Sum(Ii/SiTi)]100

where:

I=peak area corrected for background and normalized for step size

S=peak area sensitivity factor (element and electron energy levelspecific)

T=total acquisition time per data point

Infrared Spectroscopy

A portion of a sample composite ply with an area of 10 to 25 squaremicrometers was physically removed from the sample's surface and placedon an infrared transparent KBr salt crystal. Infrared transmissionsspectra were obtained using a Perkin-Elmer 1800 FTIR spectrometer and aSpectra Tech IR Plan II Microscope accessory. The scanning criteria wereas follows: scan range: 4000 to 700 cm⁻¹, resolution: 4 cm⁻¹,apodization: medium, number of scans: 32, sample and background: KBr,detector - liquid nitrogen cooled mercury/cadmium/telluride (MCT).

EXAMPLES Example 1

This Example illustrates the preparation of appropriate microcompositeunidirectional tape plies which may be subsequently treated with anacidic solvent. A microcomposite yarn of 64% by weight ofpoly(paraphenylene benzobisthiazole) (PBT) and 36% poly(etherketoneketone) (PEKK) was produced in the following manner.

In a 3.8 liter mixing vessel, 205 cc of 100% sulfuric acid, 245 cc ofpoly(phosphoric acid), and 101 cc (135.6 g) of PEKK polymer were stirredovernight at 32° C. under a nitrogen atmosphere. The mixing vessel wasthen warmed to 50° C. and 1588 g of a solution having 15% of PBT inpoly(phosphoric acid) was added. This mixture was then stirred at 50° C.for 1.5 hours. After this time, 939 cc of poly(phosphoric acid) wasadded to the mixing vessel. This mixture was then stirred overnight at56° C.

A vacuum (1 mm Hg pressure) was then applied to the mixing vessel for 3hours, while the mixture continued to be stirred. After this time, thetemperature was increased to 80° C. and the stirrer was turned off.After sitting for 1 hour, the dump valve at the mixing vessel's bottomwas opened and the vessel was pressurized with nitrogen to force thesolution out. The solution was pumped by a gear pump at a rate of 2.7cc/min through an X7 Dynalloy filter and then through an 80 holespinneret with each hole having a diameter of 0.007 inches. The extrudedfilaments passed through a 1 cm air gap and into a circulating waterbath. The temperature of the bath was maintained at 5° C. Coagulatedyarn was pulled from the bath and wound up continuously on bobbins at aspeed of 11 meters/minute.

The as-spun microcomposite yarn was then soaked in 5 gallon buckets ofwater for three days to remove the solvent. The yarn was thenheat-treated at a temperature of 375° C. in a 15 foot tube oven purgedwith nitrogen. A tension of 1.3 grams per denier (gpd) was applied tothe yarn during heat-treatment, and a residence time of 18 seconds inthe oven was used. The yarn which exited the oven was wound up oncardboard bobbins.

The microcomposite yarn was then converted into unidirectional tapeplies using the following process:

A 16"×11"×0.25" composite card, i.e., a flat plate, was covered on bothsides with a polyimide film. The card was then mounted in a windingdevice with a rotor, to which the card was mounted, and an independentlycontrolled traverse. Heat treated yarn was threaded through an automatictensioning device, through the traverse of the winder and the end of theyarn was taped to an edge of the card. The yarn was then wrapped aroundthe card with the rotor and traverse speeds controlled so as to make 70to 80 wraps per inch on the card and to keep the yarn bundles parallelto the long axis of the card. Four passes were made, covering a width of10.25" with a total of 300 wraps of yarn per inch. After winding, theyarn was cut and the cut end taped down to an edge of the card. On eachside of the card, the yarn was then covered with a piece of polyimidefilm and a 12"×17"×1/16" ferro type plate. This lay-up was then wrappedin a double layer of aluminum foil and the edges rolled tight to make aneffective seal. The package was placed in a hydraulic press and a small(1/16" diameter) tube was inserted in the foil. A nitrogen flow wasmaintained through this tube to purge the package of air. The hydraulicpress platens were then closed to a point where the card was placedunder slight positive pressure (approximately 10 psi) and then heated toa temperature of 335° C. When the platens reached a temperature of 335°C., a pressure of 150 psi was applied and maintained for ten minutes. Atthe end of ten minutes, the pressure was reduced to 10 psi and the heatto the platens was turned off. The press was then allowed to cool toroom temperature overnight.

After the card had cooled to room temperature, it was removed from thepress and the foil wrapping and ferro plates were removed. The pressedyarn was removed from the card by cutting the yarn at the card edgesusing a razor knife and carefully peeling the inner polyimide film layeraway from the card with a spatula. The polyimide film was then carefullyremoved from the consolidated microcomposite fibers by slowly peelingoff the film in a direction perpendicular to the direction of the fiber.This process yielded coherent 10.25"×16"×0.018" sheets of PBT/PEKKmicrocomposite tape with the fibers uniaxially aligned along the longaxis of the sheet.

Example 2

Using a razor blade, ten 3.5"×0.5" strips were cut from the PBT/PEKKmicrocomposite tape prepared in Example 1. These strips were cut in sucha manner that the fiber direction was parallel to the long (3.5") axisof the strips and are referred to as "0 degree strips". Additionally,two 3.5"×1.25" strips were cut with the fiber direction parallel to thelong axis of the strip.

All of the 3.5"×0.5" strips were placed in 100.05% sulfuric acid suchthat 1.75", or one-half the length, of each strip was immersed. Sixstrips were immersed for 10 seconds, and four were immersed for 20seconds. At the end of the acid immersion time, all of the strips wereremoved and completely immersed in cold water in which they were rinseduntil neutralized.

Both 3.5"×1.25" strips were similarly placed in 100.05% sulfuric acidsuch that a 2.0" section, or two thirds of the length, was immersed. Onestrip was immersed for 20 seconds and the other for 60 seconds. At theend of the acid immersion time, both strips were removed and washed withwater until they were neutralized.

Those regions of the 3.5"×0.5" and 3.5"×1.25" ply strips which were notin contact with the acidic solvent did not change colors, and had arough surface with bare fibers exposed. FIG. 1 shows such a region of a3.5"×1.25" strip. In contrast, each region of the 3.5"×0.5" and3.5"×1.25" strips which were in contact with the acidic solventunderwent a color change from an original reddish-brown to a goldencolor, and had a smooth surface indicating that the polymer matrix hadbeen deposited on the ply's surface. FIG. 2 shows a region of the plystrip of FIG. 1 which was in contact with the acidic solvent. Thesurface compositions of the treated and untreated regions of thePBT/PEKK microcomposite plies were determined by ESCA analysis and arepresented in Table 1. The elements, sulfur and nitrogen are unique toPBT. However, some sulfur may be present in the PEKK which is either dueto sulfonation or residual solvent. Therefore, the atomic percentage ofnitrogen issued as an indicator of the PBT content. If more nitrogen isdetected at the surface, it signifies that more PBT is present at thesurface. For each treated and analyzed region, the nitrogen content issignificantly reduced versus that of the untreated region. In two of thesamples, there was no detection of any nitrogen on the treated surfaces.

                  TABLE 1                                                         ______________________________________                                        Acid Treatment Atomic Concentration (%)                                       (seconds)      C     O          N   S                                         ______________________________________                                        10             80    18         0   1.4                                       20             77    18         1.1 2.8                                       60             75    20         0   2.7                                       Untreated      79    15         2.3 2.4                                       ______________________________________                                    

Several 1.0"×0.5" strips were cut from the treated regions of the3.5"×1.25" ply strips. These 1.0"×0.5 strips were cut with a fiberdirection oriented perpendicular to the long (1") axis of the strips andare referred to as "90 degree strips".

Using the treated regions of the 3.5"×0.5" ply strips, lap-shear testsamples were prepared in the following manner:

A 6"×0.5" strip of polyimide film which had been sprayed on both sideswith "Frekote" 44 mold release agent was placed on the bottom of a6"×0.5" rectangular matched die mold. A first, 3.5"×0.5", 0-degree,strip was placed on top of the polyimide film with the untreated end ofthe strip placed against the end of the mold, and the treated end placedover the center of the mold. A 1.0×0.5", 90-degree strip, was thenplaced on top of the treated end of the 0-degree strip so that itcovered the last 1 inch of the 0-degree strip. A second, 3.5"×0.5", 0degree, strip was placed on top of the 90-degree strip and the first0-degree strip with the untreated end of the strip against the end ofthe mold opposite the untreated end of the first 0-degree strip and thetreated end of the strip covering the 90-degree strip. This lay-upyielded a 6 inch long sample with the center 1 inch of the sampleconsisting of a three-ply overlap of a 90-degree ply sandwiched betweentwo 0-degree plies and is referred to as a 0/90/0 degree lay-up.

These samples were treated with acidic solvent for various time periodsas shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Acid Treatment (seconds)                                                                            Lap-Shear Strength                                      Sample                                                                              0-Degree Plies                                                                            90 Degree Ply                                                                             (PSI)                                           ______________________________________                                        1     10          10          285                                             2     20          10          243                                             3     10          20          156                                             4     20          20          410                                             5     10          60          560                                             6     0/20        60           40                                             7     0            0           0                                              ______________________________________                                    

A second "Frekote" 44 sprayed 6"×0.5" polyimide film was placed on topof the 0/90/0 degree layup and the top ram plate of the mold wasinserted. A thermocouple was placed in the mold wall and the assemblywas wrapped in aluminum foil and placed in a hydraulic press.

As the five samples were purged with nitrogen through a tube which wasinserted in the aluminum foil, the press platens were closed to apply asmall positive pressure (approximately 10 psi) to the mold and wereheated to 375° C. When the platens reached 375° C., the pressure wasincreased to 2000 psi and maintained for ten minutes. After ten minutes,the platen heaters were turned off and the platens were water cooled toreduce the temperature at a rate of approximately 10° C. per minute.Pressure was maintained until the temperature was below 140° C., atwhich point the pressure was allowed to slowly drop off as the moldcooled. The mold was removed from the press after it had cooled to below40° C.

The samples were removed from the mold and the polyimide film was peeledoff. The overlap areas of all five samples appeared well bonded. Eachsample was prepared for testing by bonding two 1/16"×1"×1/2" cardboardtabs on each end of the sample with an epoxy adhesive. The samples weretested in tension in an Instron Model No. 1122 testing frame with anInstron 1000 pound reversible load cell. All of the samples were testedwith a 4.0" gage length. Samples 1, 2, and 3 were tested with anelongation rate of 0.005 inches/minute. The elongation rate wasincreased to 0.02 inches/minute for samples 4 and 5 in order to overcomethe observed tab slipping which occurred at low strain rates. The lapshear strengths were determined by dividing the ultimate load (in poundsforce) at which the bond failed by the bond area, which was 0.5 squareinches in all cases. Measured lap shear strengths ranged from a lowestvalue of 156 psi to a highest value of 558 psi, as listed in Table 2.The failed test samples showed evidence of plastic deformation andpull-out of matrix at the failed interface which are indications thatthe two surfaces were well bonded together.

Example 3

A PBT/PEKK microcomposite, 0/90/0 degree, lap shear sample was preparedusing the same procedures as described in Example 2, except that one ofthe 0-degree plies used was not treated with the acid solvent. The other0-degree ply was treated for 20 seconds in sulfuric acid and the90-degree ply was soaked in sulfuric acid for 60 seconds.

The sample was prepared, molded and tabbed under the same conditionsdescribed for the samples in Example 2. The sample was tested in tensionusing the same conditions described for the samples of Example 2 and islisted as Sample 6 in Table 2. The sample failed at a bond strength ofonly 40 psi and failed on the interface between the 90-degree ply andthe untreated 0-degree ply. Microscopic examination of the failedinterface showed no evidence of plastic deformation or adhesive bonding.

Example 4

PBT/PEKK microcomposite, 0/90/0 degree, lap shear samples were preparedusing the same procedures as described in Example 2, except that none ofthe plies in the samples were treated with acid. The samples were moldedunder a number of conditions, including those described for the samplesin Example 2, with pressures ranging from 1000 to 6000 psi andtemperatures ranging from 350° to 450° C. In each case, the adhesion wasso poor that the samples either did not bond and fell apart when removedfrom the mold, or were so loosely bonded that they could not be handledand tabbed for mechanical testing as shown by Sample 7 in Table 2.

Example 5

A microcomposite yarn of 69% by weight of PBT and 31% of a thermoplasticpolyamide was prepared according to the following procedure. Thethermoplastic polyamide was an amorphous copolymer of hexamethylenediamine, isophthalic and terephthalic acids in a 100/70/30 mol percentbasis.

1,157 grams of methanesulfonic acid (MSA) and 39 grams ofpoly(phosphoric acid) (PPA) were mixed in a beaker and poured into a 3.8liter mixer. Mixing was continued inside the mixing vessel at 30 rpmunder a nitrogen atmosphere. 88.7 grams of the dried polyamide wereadded and mixed overnight to assure complete dissolution. Thetemperature of the solution was measured during the next morning andfound to be 50° C. This rise in temperature from room temperature to 50°C. was due mainly to the mechanical action from the mixing. 1,315 gramsof a 15% by weight PBT/ 85% PPA dope were added to the solution andmixed for seven days. The resulting highly viscous dope was transferredto a spin cell, attached to the bottom opening of the mixer. Thisviscous dope was deaerated by extruding from the first cell, through athin slot, and into the vacuum chamber of a second cell at 50° C.Microcomposite yarns were air-gap spun at 60° C., at a rate of 9meters/minute using a 80-hole spinneret having 4-mil diameter holes intoan ice bath.

The heat-treated, feed yarn (290 filaments, 500 denier) was wound off afeed bobbin, fed through a tension gate and into an 100.05% sulfuricacid solvent bath. After leaving the acid bath, the yarn passed througha water coagulation bath and then into an aqueous ammonium hydroxideneutralization bath. The treated yarn was then wound up on a bobbinwhich was kept wet with a water spray to further effect solvent removal.The solvent contact time was controlled by varying the acid contactlength and the throughput rate. The acid contact length is defined asthe length of the threadline from the point of entry into the acid bathto the point of entry into the coagulation bath and the throughput rateis defined as the velocity of the threadline. The yarn was treated witha solvent contact time of 8.8 seconds (1.83 feet acid contact length,12.5 feet/min throughput rate). After this treatment, the yarn wasbackground through a tube furnace at 200° C. in order to retry the yarn.The untreated, feed yarn could easily be separated into individualfilaments and were not highly fused together, as shown in FIG. 3.However, after solvent treatment and removal the same yarn had theappearance of a thin (approximately 1/16" wide) tape and the filamentsof the yarn were highly fused together by a coating of polymer matrix,as shown in FIG. 4. Furthermore, only a small amount of material waslost, as evidenced by a less than two percent (<2%) reduction in denierof the treated yarn versus the untreated yarn.

This treated PBT/polyamide microcomposite yarn was wrapped around analuminum card and pressed to make a unidirectional tape according to theprocess described in Example 1. This tape was then cut and used toproduce three 0/90/0 degree lap shear test samples according to theprocess described in Example 2. The samples were compression molded at atemperature of 335° C. and a pressure of 1500 psi. These samples had anaverage lap shear strength of 423 psi.

Example 6

Some untreated PBT/polyamide microcomposite yarn of Example 5 was usedto form 0/90/0 degree lap shear samples according to the processesdescribed in Examples 1 and 2. The samples were compression molded underthe same conditions described in Example 5 (325° C./1500 psi). Theseuntreated samples had an average lap shear strength of 250 psi.

Example 7

A microcomposite yarn of 63% by weight of PBT and 37% polyimide wasprepared according to the following process:

A quaternary spin dope containing PBT and the polyamic acid having therepeat unit, ##STR1##

was first prepared. This spin dope was prepared as follows:

9.43 grams of polyamic acid and 82.9 grams of methanesulfonic acid wereloaded into an Atlantic mixer and stirred overnight at room temperatureunder an inert atmosphere to form a solution. 113.0 grams of a 15% byweight PBT/85% poly(phosphoric acid) (PPA) dope were added to thesolution. The mixture was then stirred overnight at 53° C., and then at62° C. for 2.5 hours. The spin dope was then transferred to a first spincell. To effect deaeration, the dope was transferred to a second spincell by extrusion under vacuum through a slit die. The dope was thenspun through a 10-hole spinneret with each hole having a 0.007 inchdiameter at 2.1 meters/minute. The dope passed through a 1.3 cm air-gapat 75° C. and into a room temperature water bath. The yarn was wound uponto a bobbin with a spin stretch factor of 4.9. The bobbin was soakedin water for one day to completely extract residual spin solvent andthen air-dried. Analysis of the yarn indicated that greater than 90percent of the polyamic acid had been converted to polyimide.

The as-spun yarn was wound around an aluminum card which had beencovered with a polyimide film to form a unidirectional sheet accordingto the process described in Example 1. This sheet was then pressed at355° C., 200 psi under nitrogen to consolidate it into a tape. The tapewas then cut into 6"×0.5" strips. Four strips were solvent treated bypainting, i.e., brushing, the surface with 100.05% sulfuric acid,allowing the acid to stand for 10 seconds, and then rinsing thoroughlywith water. These strips were then used to produce two uniaxial two-plylap shear test samples according to the process described in Example 2.The samples were compression molded at a temperature of 425° C. and apressure of 2000 psi under nitrogen.

The samples had an average lap shear strength of 180.5 psi. The failedspecimens exhibited a significant amount of fiber pull-out across theinterface, indicating that the two surfaces were well bonded together.

Example 8

Some untreated PBT/polyimide yarn of Example 7 was used to prepareuniaxial lap shear test samples according to the processes described inExamples 1 and 2. The samples were compression molded under the sameconditions described in Example 7 (425° C./2000 psi under nitrogen).These untreated samples had an average lap shear strength of 118 psi andfailed cleanly, with no evidence of plastic deformation or adhesivefailure.

Example 9

Sheets of microcomposite plies were made by winding microcomposite fiberof 69% by weight of PBT and 31% of an amorphous thermoplastic polyamideon a 6.5" by 6.5" aluminum plate in the same direction. Thethermoplastic polyamide was an amorphous copolymer of hexamethylenediamine, isophthalic and terephthalic acids in a 100/70/30 mol percentbasis. The 69% PBT/ 31% polyamide microcomposite fiber was madeaccording to the following procedures.

1,157 grams of methanesulfonic acid (MSA) and 39 grams ofpoly(phosphoric acid) (PPA) were mixed in a beaker and poured into a 3.8liter mixer. Mixing was continued inside the mixing vessel at 30 rpmunder a nitrogen atmosphere. 88.7 grams of the dried polyamide wereadded and mixed overnight to assure complete dissolution. Thetemperature of the solution was measured during the next morning andfound to be 50° C. This rise in temperature from room temperature to 50°C. was due mainly to the mechanical action from the mixing. 1,315 gramsof a 15% by weight PBT/ 85% PPA dope were added to the solution andmixed for seven days. The resulting highly viscous dope was transferredto a spin cell, attached to the bottom opening of the mixer. Thisviscous dope was deaerated by extruding from the first cell, through athin slot, and into the vacuum chamber of a second cell at 50° C.Microcomposite yarns were air-gap spun at 60° C., at a rate of 9meters/minute using a 80-hole spinneret having 4-mil diameter holes intoan ice bath.

A layer of polyimide film ,"Kapton", available from E.I. du Pont deNemours and Co., Inc. was placed on the aluminum plate before and afterthe yarns were wound. The aluminum plate was placed in a vacuum pressand the wound fibers were consolidated at a temperature of 300° C. and apressure of 293 psi into a sheet product. Ply strips measuring 0.5"(width) by 6.0" (length) were cut from the consolidated sheets at 90degrees and also at 0 degrees to the direction of the fiber. Thefollowing sequence of steps were used to extract the thermoplasticmatrix from the ply strips:

Two strips of the 0 degree plies were dipped half way into 100%concentrated methanesulfonic acid (MSA) solvent. The untreated halvesbecame the control samples. Excess MSA was applied using an eye dropperon the treated halves of the strips and the strips were held horizontalfor 3-4 minutes. Afterwards, the strips were placed in a beaker ofdistilled water to remove the MSA solvent. The MSA solvent was furtherremoved by immersing the strips in another beaker of fresh distilledwater for two days. Afterwards, the strips were immersed in distilledwater having a pH adjusted to 10.5 by using ammonium hydroxide. This wasfollowed by rinsing the strips in distilled water again and letting thestrips air dry.

A three layer composite ply strip was prepared by sandwiching anuntreated 90 degree strip between the two solvent treated 0 degreestrips and placing the layer of strips in a 0.5"×6.0" mold. A layer of"Kapton" film was placed on top and below the layer of strips.Consolidation was done in a vacuum at 300° C. with pressure up to 747psi. The final consolidated 0/90/0 degree, 0.5"×6.0", composite plystrip was cut at the center to separate the control from the solventtreated regions. A 0.5"×3.0" lap-shear specimen was prepared for eachcontrol and solvent treated sample by removing certain areas of theplies such that a 0.5"×0.25" 90 degree strip covered one end of a bottom0.5"×1.625" 0 degree strip, and a second, 0.5"×1.625" 0 degree stripcovered the top of the 0.5"×0.25" 90 degree strip. The lap-shearstrength of the 0.5"×0.25" overlapping area was measured by clamping thealuminum tabbed ends of the specimen in an Instron tensile tester (Model1122). The lap-shear strength of the control sample was 230 psi, whilethe solvent treated sample had a lap-shear strength of 318 psi.

Example 10

Four, 0.5"×3.0", 0 degree strips and two, 0.5"×3.0" 90 degree ply stripswere cut from the microcomposite sheet of Example 9. The strips weretreated with solvent in the same manner as described in Example 9,except that the solvent used was 89.7% concentrated MSA, and the stripswere completely treated with solvent. The control strips were madeseparately from the same microcomposite sheets as the solvent treatedstrips. At this concentration, the solvent will selectively dissolve thepolyamide polymer matrix but will not dissolve the PBT.

The strips were rinsed free of the acid solvent and air dried asdescribed in Example 9. Additionally, the strips were vacuum oven driedat 97° C. for 3 days. A white coating was observed to cover the surfaceof the solvent-treated strips, whereas the control strips remained darkbrown. A sample of this white coating was scraped and analyzed byinfrared spectroscopy (IR), and found to have identical spectra as thatof the pure polyamide matrix. Two, 0/90/0 degree, lap-shear specimenswere prepared and tested in the same manner as described in Example 9.The lap-shear strengths of the solvent treated samples were 476 psi and774 psi. The average lap-shear strength for the control samples was 319psi.

Example 11

Sheets of microcomposite plies were made by winding microcomposite fiberof 70% by weight of poly(p-phenylene terephthalamide) and 30% of anamorphous thermoplastic polyamide, in the same manner as described inExample 9. The thermoplastic polyamide was an amorphous copolymer ofhexamethylene diamine, (20tt) bis(p-amino-cyclohexyl)methane,isophthalic, and terephthalic acids in a 96/4/70/30 mol percent basis.The strips were treated with solvent in the same manner as described inExample 9, except that the solvent used was 89.7% concentrated MSA, andthe solvent contact time for the samples varied as shown in Table 3. Thelap-shear samples were made and tested in the same manner as describedin Example 9. The lap-shear strengths for the control and solventtreated samples are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Acid    Acid                                                                  Treatment                                                                             Treatment Lap-Shear Control Lap-Shear                                 Sample  (Minutes) Strength  Sample  Strength                                  ______________________________________                                        1       1         840 psi   1       300 psi                                   2       3         840 psi   2       364 psi                                   3       6         744 psi   3       337 psi                                   ______________________________________                                    

We claim:
 1. An oriented, shaped microcomposite article, comprising atleast about 30% and less than about 80% by weight of a reinforcingpolymer phase consisting essentially of at least one lyotropic polymer,and at least about 20% and less than about 70% by weight of a polymermatrix consisting essentially of at least one thermally-consolidatablepolymer, said reinforcing polymer phase being continuous in thedirection of orientation while interpenetrating said polymer matrixthroughout the article, said article having a decreasing concentrationgradient of polymer matrix from the article's surface to the article'sinterior.
 2. An oriented, shaped micro composite article of claim 1,wherein said lyotropic polymer is a para-aramid.
 3. An oriented, shapedcomposite article of claim 1, wherein said lyotropic polymer is anaromatic-heterocyclic polymer.
 4. An oriented, shaped micro compositearticle of claim 1, wherein said thermally-consolidatable polymer isselected from the class consisting of thermoplastic polyamides.
 5. Anoriented, shaped micro composite article of claim 1, wherein saidlyotropic polymer is a para-aramid, and said thermally-consolidatablepolymer is selected from the class consisting of thermoplastic polymers.6. An oriented, shaped micro composite article of claim 1, wherein saidlyotropic polymer is a para-aramid, and said thermally-consolidatablepolymer is selected from the class consisting of thermoplasticpolyamides.
 7. An oriented, shaped micro composite article of claim 1,wherein said lyotropic polymer is an aromatic-heterocyclic polymer, andsaid thermally-consolidatable polymer is selected from the classconsisting of thermoplastic polymers.
 8. An oriented, shaped microcomposite article of claim 1, wherein said lyotropic polymer is anaromatic-heterocyclic polymer, and said thermally-consolidatable polymeris selected from the class consisting of thermoplastic polyamides.
 9. Anoriented, shaped micro composite article of claim 1, wherein saidthermally-consolidatable polymer is a polyimide.
 10. An oriented, shapedmicro composite article of claim 1, wherein the article is in the formof a fiber.
 11. An oriented, shaped micro composite article of claim 1,wherein the reinforcing polymer phase and polymer matrix areco-continuous.
 12. An oriented, shaped micro composite article of claim1, wherein said thermally-consolidatable polymer is selected from theclass consisting of thermoplastic polymers.
 13. An oriented, shapedmicro composite article of claim 12, wherein said thermoplastic polymeris poly(ether ketoneketone).
 14. A micro composite ply, comprising atleast about 30% and less than about 80% by weight of a reinforcingpolymer phase consisting essentially of at least one lyotropic polymer,and at least about 20% and less than about 70% by weight of a polymermatrix consisting essentially of at least one thermally-consolidatablepolymer, said reinforcing polymer phase being continuous in thedirection of orientation while interpenetrating said polymer matrixthroughout the ply, said ply having a decreasing concentration gradientof polymer matrix from the ply's surface to the ply's interior.
 15. Amicro composite ply of claim 14, wherein said lyotropic polymer is apara-aramid.
 16. A micro composite ply of claim 14, wherein saidlyotropic polymer is an aromatic-heterocyclic polymer.
 17. A microcomposite ply of claim 14, wherein said thermally-consolidatable polymeris selected from the class consisting of thermoplastic polyamides.
 18. Amicro composite ply of claim 14, wherein said lyotropic polymer is apara-aramid, and said thermally-consolidatable polymer is selected fromthe class consisting of thermoplastic polymers.
 19. A micro compositeply of claim 14, wherein said lyotropic polymer is a para-aramid, andsaid thermally-consolidatable polymer is selected from the classconsisting of thermoplastic polyamides.
 20. A micro composite ply ofclaim 14, wherein said lyotropic polymer is an aromatic-heterocyclicpolymer, and said thermally-consolidatable polymer is selected from theclass consisting of thermoplastic polymers.
 21. A micro composite ply ofclaim 14, wherein said lyotropic polymer is an aromatic-heterocyclicpolymer, and said thermally-consolidatable polymer is selected from theclass consisting of thermoplastic polyamides.
 22. A micro composite plyof claim 14, wherein aid thermally-consolidatable polymer is apolyimide.
 23. A micro composite ply of claim 14, wherein thereinforcing polymer phase and polymer matrix are co-continuous.
 24. Alaminate, comprising the micro composite ply of claim
 14. 25. A microcomposite ply of claim 14, wherein said thermally-consolidatable polymeris selected from the class consisting of thermoplastic polymers.
 26. Amicro composite ply of claim 25, wherein said thermoplastic polymer ispoly(ether ketoneketone).